Demonstration of magnetic field tomography with starlight polarization towards a diffuse sightline of the ISM
Georgia V. Panopoulou, Konstantinos Tassis, Raphael Skalidis, Dmitriy Blinov, Ioannis Liodakis, Vasiliki Pavlidou, Stephen B. Potter, Anamparambu N. Ramaprakash… 展开作者
Georgia V. Panopoulou, Konstantinos Tassis, Raphael Skalidis, Dmitriy Blinov, Ioannis Liodakis, Vasiliki Pavlidou, Stephen B. Potter, Anamparambu N. Ramaprakash, Anthony C. S. Readhead, Ingunn K. Wehus
备注：
25 pages, 14 figures, published in ApJ, data appear in journal
The availability of large datasets with stellar distance and polarization information will enable a tomographic reconstruction of the (plane-of-the-sky-projected) interstellar magnetic field in the near future. We demonstrate the feasibility of such a decomposition within a small region of the diffuse ISM. We combine measurements of starlight (R-band) linear polarization obtained using the RoboPol polarimeter with stellar distances from the second Gaia data release. The stellar sample is brighter than 17 mag in the R band and reaches out to several kpc from the Sun. HI emission spectra reveal the existence of two distinct clouds along the line of sight. We decompose the line-of-sight-integrated stellar polarizations to obtain the mean polarization properties of the two clouds. The two clouds exhibit significant differences in terms of column density and polarization properties. Their mean plane-of-the-sky magnetic field orientation differs by 60 degrees. We show how our tomographic decomposition can be used to constrain our estimates of the polarizing efficiency of the clouds as well as the frequency dependence of the polarization angle of polarized dust emission. We also demonstrate a new method to constrain cloud distances based on this decomposition. Our results represent a preview of the wealth of information that can be obtained from a tomographic map of the ISM magnetic field.
Diffuse interstellar bands (DIBs) can trace different conditions of the ISM along the sightline toward the observed stars. A small survey was made in optical wavelengths, producing high resolution and high signal to noise spectra. We present measurements of 19 DIBs' properties in 50 sightlines towards hot stars, distributed at a variety of galactic coordinates and interstellar reddening. Equivalent widths were obtained by fitting asymmetric Gaussian and variable continuum to DIBs. Conditions of the ISM were calculated from 8 atomic and molecular interstellar lines. Two distinctively different …
The precise characteristics of clouds and the nature of dust in the diffuse interstellar medium can only be extracted by inspecting the rare cases of single-cloud sightlines. In our nomenclature such objects are identified by interstellar lines, such as K I, that show at a resolving power of $λ/Δλ\sim 75,000$ one dominating Doppler component that accounts for more than half of the observed column density. We searched for such sightlines using high-resolution spectroscopy towards reddened OB stars for which far-UV extinction curves are known. We compiled a sample of 186 spectra, 100 of which we…
In a survey of archived ultraviolet spectra of 100 stars recorded by the echelle spectrograph of the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), we measure the strengths of the weak absorption features of O I, Ge II and Kr I in the interstellar medium. Our objective is to undertake an investigation that goes beyond earlier abundance studies to see how these elements are influenced independently by three different environmental properties: (1) values of a generalized atomic depletion factor $F_*$ due to condensations onto dust grains (revealed here by the ab…
Context: Nearly one century after their discovery, the carrier(s) of Diffuse Interstellar Bands is/are still unknown and there are few sightlines studied in detail for a large number of DIBs. Aims: We want to study the ISM sightlines towards LS III +46 11 and LS III +46 12, two early-O-type stellar systems, and LS III +46 11 B, a mid-B-type star. The three targets are located in the stellar cluster Berkeley 90 and have a high extinction. Methods: We use the multi-epoch high-S/N optical spectra presented in paper I (Maíz Apellániz et al. 2015), the extinction results derived there, and addition…
Studying the composition of dust in the interstellar medium (ISM) is crucial in understanding the cycle of dust in our galaxy. The mid-infrared spectral signature of amorphous silicates, the most abundant dust species in the ISM, is studied in different lines-of-sight through the Galactic plane, thus probing different conditions in the ISM. We have analysed 10 spectra from the Spitzer archive, of which 6 lines-of-sight probe diffuse interstellar medium material and 4 probe molecular cloud material. The 9.7 um silicate absorption features in 7 of these spectra were studied in terms of their sha…
Observations of interstellar dust are often used as a proxy for total gas column density $N_\mathrm{H}$. By comparing $\textit{Planck}$ thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS (Green et al. 2018), with accurate (opacity-corrected) HI column densities and newly-published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth $τ_{353}$, reddening $E(B{-}V)$ and the total proton column density $N_\mathrm{H}$ in the range (1$-$30)$\times$10$^{20}$cm$^{-2}$, along sightlines with no molecula…
Interstellar Polarization Survey. IV. Characterizing the magnetic field strength and turbulent dispersion using optical starlight polarization in the diffuse interstellar medium
本文利用 IPS-GI 光学星光偏振与 GASS 的 HI 分解，评估角色散函数在近邻弥漫 ISM 中的适用性，并测绘天空平面磁场、密度及湍流速度弥散。
We present the first Bayesian method for tomographic decomposition of the plane-of-sky orientation of the magnetic field with the use of stellar polarimetry and distance. This standalone tomographic inversion method presents an important step forward in reconstructing the magnetized interstellar medium (ISM) in 3D within dusty regions. We develop a model in which the polarization signal from the magnetized and dusty ISM is described by thin layers at various distances. Our modeling makes it possible to infer the mean polarization (amplitude and orientation) induced by individual dusty clouds a…
The interstellar magnetic field (ISMF) near the heliosphere is a basic part of the solar neighborhood that can only be studied using polarized starlight. Results of an ongoing survey of polarized starlight are analyzed with the goal of linking the interstellar magnetic field that shapes the heliosphere to the nearby field in interstellar space. New results for the direction of the nearby ISMF, based on a merit function that utilizes polarization position angles, identify several magnetic components. The dominant interstellar field, B_pol, is aligned with the direction L,B= 36.2,49.0 (+/-16.0) …
We map the interstellar medium (ISM) including the diffuse interstellar bands (DIBs) in absorption toward the globular cluster NGC 6397 using VLT/MUSE. This pilot study demonstrates the power of MUSE for mapping the local ISM on very small scales which provides a new window for ISM observations. Assuming the absorbers are located at the rim of the Local Bubble we trace small-scale variations in NaI and KI as well as in several DIBs structures on the order of mpc (milliparsec, a few thousand AU). The sightlines defined by binned stellar spectra are separated by only a few arcseconds and we prob…
3D B-fieLds in the InterStellar medium and Star-forming regions (3D-BLISS): I. Using Starlight Polarization in the Massive IRDC Filament G11.11-0.12
Korea Astronomy and Space Science Institute（韩国天文学与空间科学研究所）；University of Science and Technology（科学技术大学）；Vietnam National Space Center（越南国家航天中心）；Vietnam Academy of Science and Technology（越南科学技术院）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）
We compare observations of HI from the Very Large Array (VLA) and the Arecibo Observatory and observations of HCO$^+$ from the Atacama Large Millimeter/submillimeter Array (ALMA) and the Northern Extended Millimeter Array (NOEMA) in the diffuse ($A_V\lesssim1$) interstellar medium (ISM) to predictions from a photodissociation region (PDR) chemical model and multi-phase ISM simulations. Using a coarse grid of PDR models, we estimate the density, FUV radiation field, and cosmic ray ionization rate (CRIR) for each structure identified in HCO$^+$ and HI absorption. These structures fall into two c…
Measuring Interstellar Carbon Abundance via 158 um [CII] Absorption with SOFIA -- A Potential Detection, and Proof-of-Concept for Depletion Studies with Future Far-IR Facilities
A key indicator of the galactic environment of the Sun is provided by the magnetic field in the interstellar medium (ISM), which influences the shape of the heliosphere. The direction of the nearby interstellar magnetic field (ISMF) is determined from starlight polarized in the ISM. The local ISMF direction is found from the ISMF direction that provides the best fit to the polarization position angles of nearby stars, using weighted fits to the data. New polarization observations are included in the analysis. The best-fitting ISMF is close to the magnetic field direction traced by the center o…
Dust permeates the interstellar medium, reddening and polarizing background starlight, but dust properties vary with local environment. In order to characterize dust in a highly irradiated diffuse cloud, we measure the reddening and optical polarization towards 27 stars surrounding the mid-latitude $b$=$+$24$^{\circ}$ O9.2IV star $ζ$ Ophiuchi, using new optical spectroscopy and polarimetry. We incrementally deredden and depolarize with distance, allowing us to distinguish dust components along these sightlines. The data indicate three distinct dust populations: a foreground component character…
Variations in the spatial configuration of the interstellar magnetic field (ISMF) near the Sun can be constrained by comparing the ISMF direction at the heliosphere found from the Interstellar Boundary Explorer spacecraft (IBEX) observations of a 'Ribbon' of energetic neutral atoms (ENAs), with the ISMF direction derived from optical polarization data for stars within ~40 pc. Using interstellar polarization observations towards ~30 nearby stars within 90 deg of the heliosphere nose, we find that the best fits to the polarization position angles are obtained for a magnetic pole directed towards…
Magnetism is one of the most important forces on the interstellar medium (ISM), anisotropically regulating the structure and star formation that drive galactic evolution. Recent high dynamic range observations of diffuse gas and molecular clouds have revealed new links between interstellar structures and the ambient magnetic field. ISM morphology encodes rich physical information, but deciphering it requires high-resolution measurements of the magnetic field: linear polarization of starlight and dust emission, and Zeeman splitting. These measure different components of the magnetic field, and …
Starlight that becomes linearly polarized by magnetically aligned dust grains provides a viable diagnostic of the interstellar magnetic field (ISMF). A survey is underway to map the local ISMF using data collected at eight observatories in both hemispheres. Two approaches are used to obtain the magnetic structure: statistically evaluating magnetic field directions traced by multiple polarization position angles, and least-squares fits that provide the dipole component of the magnetic field. We find that the magnetic field in the circumheliospheric interstellar medium (CHM), which drives winds …
Magnetic fields permeate the entire Galaxy and are essential to, for example, the regulation of several stages of the star formation process and cosmic ray transportation. Unraveling its properties, such as intensity and topology, is an observational challenge that requires combining different and complementary techniques. The polarization of starlight due to the absorption by field-aligned non-spherical dust grains provides a unique source of information about the interstellar magnetic field in the optical band. This work introduces a first analysis of a new catalog of optical observations of…
Three-dimensional (3D) maps of the Galactic interstellar matter (ISM) are a potential tool of wide use, however accurate and detailed maps are still lacking. One of the ways to construct the maps is to invert individual distance-limited ISM measurements, a method we have here applied to measurements of stellar color excess in the optical. We have assembled color excess data together with the associated parallax or photometric distances to constitute a catalog of ~ 23,000 sightlines for stars within 2.5 kpc. The photometric data are taken from Stromgren catalogs, the Geneva photometric database…
TRIShUL: Technique for Reconstructing magnetic Interstellar Structure Using starLight polarization
Institute of Astrophysics, Foundation for Research and Technology-Hellas（希腊研究与技术基金会天体物理研究所）；Department of Physics and Institute of Theoretical and Computational Physics, University of Crete（克里特大学物理系与理论与计算物理研究所）；Université Libre de Bruxelles（布鲁塞尔自由大学）
As a complement to the HyGAL Stratospheric Observatory for Infrared Astronomy Legacy Program, we report the results of a ground-based absorption line survey of simple molecules in diffuse and translucent Galactic clouds. Using the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescope, we surveyed molecular lines in the 2 mm and 3 mm wavelength ranges toward 15 millimeter continuum sources. These sources, which are all massive star-forming regions located mainly in the first and second quadrants of the Milky Way, form the subset of the HyGAL sample that can be observed by the IRAM 30 …
We study the effects of local environmental conditions affecting the diffuse interstellar band (DIB) carriers within the Upper Scorpius subgroup of the Sco OB2 association. We obtained optical spectra with FEROS, and measured the equivalent widths of five DIBs (at 5780, 5797, 6196, 6379, and 6613 Angstrom) as well as those of absorption lines of di-atomic molecules (CH, CH+, CN) and atoms (KI, CaI) towards 89 targets in the direction of Upper Scorpius. We construct a simple radiative transfer and chemical network model of the diffuse interstellar medium (ISM) sheet in front of Upp Sco to infer…
A first taste of MEAD (Measuring Extinction and Abundances of Dust) -- I. Diffuse Milky Way interstellar dust extinction features in JWST infrared spectra
Measuring the temperature and abundance patterns of clouds in the interstellar medium (ISM) provides an observational basis for models of the physical conditions within the clouds, which play an important role in studies of star and planet formation. The Colorado High-resolution Echelle Stellar Spectrograph (CHESS) is a far ultraviolet rocket-borne instrument designed to study the atomic-to-molecular transitions within diffuse molecular and translucent cloud regions. The final two flights of the instrument observed $β^{1}$ Scorpii ($β$ Sco) and $γ$ Arae. We present flight results of interstell…
We have detected a broad interstellar absorption band centred close to 7700 Å and with a FWHM of 176.6$\pm$3.9 Å. This is the first such absorption band detected in the optical range and is significantly wider than the numerous diffuse interstellar bands (DIBs). It remained undiscovered until now because it is partially hidden behind the A telluric band produced by O$_2$. The band was discovered using STIS@HST spectra and later detected in a large sample of stars of diverse type (OB stars, BA supergiants, red giants) using further STIS and ground-based spectroscopy. The EW of the band is measu…
Faraday tomography of a field centred on the extragalactic point source 3C 196 with the LOw Frequency ARray (LOFAR) revealed an intertwined structure of diffuse polarised emission with straight depolarisation canals and tracers of the magnetized and multi-phase interstellar medium (ISM), such as dust and line emission from atomic hydrogen (HI). This study aims at extending the multi-tracer analysis of LOFAR data to three additional fields in the surroundings of the 3C 196 field. For the first time, we study the three-dimensional structure of the LOFAR emission by determining the distance to th…
We study the interaction of feedback from active galactic nuclei (AGN) and a multi-phase interstellar medium (ISM), in simulations including explicit stellar feedback, multi-phase cooling, accretion-disk winds, and Compton heating. We examine radii ~0.1-100 pc around a black hole (BH), where the accretion rate onto the BH is determined and where AGN-powered winds and radiation couple to the ISM. We conclude: (1) The BH accretion rate is determined by exchange of angular momentum between gas and stars in gravitational instabilities. This produces accretion rates ~0.03-1 Msun/yr, sufficient to p…
Diffuse interstellar bands are usually observed in spectra of hot stars, where interstellar lines are rarely blended with stellar ones. The need for hot stars is a strong limitation in the number of sightlines we can observe and the distribution of sightlines in the Galaxy, as hot stars are rare and concentrated in the Galactic plane. We are introducing a new method, where interstellar lines can be observed in spectra of cool stars in large spectroscopic surveys. The method is completely automated and does not require prior knowledge of the stellar parameters. If known, the stellar parameters …
If a single line of sight (LOS) intercepts multiple dust clouds of different spectral energy distributions and magnetic field orientations, the frequency scaling of each of the Stokes $Q$ and $U$ parameters of thermal dust emission may be different ("LOS frequency decorrelation"). We present first evidence for LOS frequency decorrelation in $Planck$ data. We use independent, neutral-hydrogen--measurements of the number of clouds per LOS and the magnetic field orientation in each cloud to select two sets of sightlines: (i) a target sample (pixels likely to exhibit LOS frequency decorrelation); …
The far-ultraviolet (FUV) diffuse emission is predominantly due to scattering of starlight from interstellar dust grains which shows a large regional variation depending on the relative orientations of dust and stars. The observations of the FUV (1000 -- 1150 Å) diffuse radiation in the Magellanic Clouds (MCs) using serendipitous observations made with the Far Ultraviolet {\em Spectroscopic Explorer (FUSE)} are presented. The estimated contribution of FUV diffuse radiation to the total integrated FUV emission in the MCs is found to be typically 5% -- 20% in the Large Magellanic Cloud (LMC) and…
The multiphase interstellar medium as a common origin for magnetic misalignment and TB parity violation
LUX, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS（巴黎天文台，巴黎文理研究大学，索邦大学）；INAF – Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切里天文台）；Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris（巴黎高等师范学院物理实验室，巴黎文理研究大学，索邦大学）；Department of Physics, California Institute of Technology（加州理工学院物理系）；TAPIR, California Institute of Technology（加州理工学院理论天体物理学与相对论研究中心）
